Multiple layers, including electrode layers, have to be applied to support structures, such as plate or tubular sensing elements made of an ion conductive solid electrolyte in order to utilize the characteristic of the electrolyte to determine the gas composition, typically the composition of exhaust gases resulting from combustion processes, for example the exhaust gases from internal combustion engines, and especially to determine the oxygen content therein. Such sensors, referred to also as lambda sensors, and which provide output voltages which change in dependence on the composition of a test gas with respect to a reference gas, usually are so made that a pre-sintered solid electrolyte body has an electrode layer applied thereto which is then sintered on the body. The surface of the body, with the electrode layer thereon which is exposed to the exhaust gas is then covered with a ceramic cover coating which is porous and which, once more, is sintered or which is plasma-sprayed only. The electrode at the opposite surface of the body, for example at the interior of a tubular structure, and which is normally exposed to a reference gas, for example ambient air, has an electrode applied thereto, but usually does not have a protective cover layer applied thereover.
It has been found that the electrodes of such sensors cannot be sufficiently loaded with electrical current, that is, the level of current loading was not adequate. This is particularly applicable with respect to the inner electrodes of tubular bodies. The electrical loading is particularly important during the start-up phase of operation of such sensors. The sensors, preferably, should be so constructed or formed that they will be fully operable at a temperature of already 300.degree. C. As the temperature drops, the O.sup.2- ion conductivity of customary solid electrolyte material drops rapidly, that is, the inner or interior inherent resistance of the sensor increases correspondingly. If high electrode polarization is added by electrodes which can be loaded only inadequately, the sensor can operate reliably and free from disturbances only at higher temperatures unless expensive and complex evaluation electronic systems are used in connection therewith.